Methods to improve efficiency of lithium/silver vanadium oxide cell discharge energy in implantable medical device applications

Abstract

It is known that reforming implantable defibrillator capacitors at least partially restores and preserves their charging efficiency. An industry-recognized standard is to reform implantable capacitors by pulse discharging the connected electrochemical cell about once every three months throughout the useful life of the medical device. A Li / SVO cell typically powers such devices. The present invention relates to methodologies for accurately determining the precise boundaries of voltage delay and irreversible Rdc growth region in the about 25% to 70% DOD region so that more frequent pulse discharging for the purpose of cell reform is confined to the limits of the region. At the same time, the connected capacitors in the cardiac defibrillator are reformed to maintain them at their rated breakdown voltages.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority based on provisional application Ser. No. 60 / 446,150, filed Feb. 10, 2003.BACKGROUND OF INVENTION[0002]1. Field of the Invention[0003]The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, this invention relates to an alkali metal / solid cathode electrochemical cell having reduced voltage delay and irreversible Rdc growth. A preferred couple is a lithium / silver vanadium oxide (Li / SVO) cell. In such cells, it is desirable to reduce voltage delay and permanent or irreversible Rdc growth at about 25% to 70% depth-of-discharge (DOD) where these phenomena typically occur.[0004]2. Prior Art[0005]Voltage delay is a phenomenon typically exhibited in an alkali metal / solid cathode cell, such as of lithium / silver vanadium oxide couple, that has been depleted of about 25% to 70% of its capacity and is subjected to high current pulse discharge applications. I...

AI Technical Summary

Benefits of technology

[0010]It is known that reforming implantable defibrillator capacitors at least partially restores and preserves their charging efficiency. An industry-recognized standard is to reform implantable capacitors by pulse discharging the connected electrochemical cell about once every 90 to 180 days throughout the useful life of the medical device. Further, conditioning methodologies for significantly minimizing, if not entirely eliminating, the occurrence of voltage delay and irreversible Rdc growth in the about 25% to 70% DOD region of a Li / SVO cell are known. These conditioning methodologies typically require the cell to be pulse discharged more frequently than that needed for reforming an implantable capacitor. The present invention is directed to determining precisely when to begin and end this more frequent pulse discharging so that cell capacity is preserved.

Problems solved by technology

Thus, decreased discharge voltages and the existence of voltage delay are undesirable characteristics of an alkali metal / silver vanadium oxide cell subjected to current pulse discharge conditions in terms of their influence on devices such as implantable medical devices including pacemakers and automatic implantable cardiac defibrillators.

Depressed discharge voltages and voltage delay are undesirable because they limit the effectiveness and even the proper functioning of both the cell and the associated electrically powered device under current pulse discharge conditions.

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